The present invention relates generally to the structure and use of radio frequency electrosurgical probes for the treatment of solid tissue. More particularly, the present invention relates to an electrosurgical probe having multiple tissue-penetrating electrodes which are deployed in an array to treat large volumes of tissue, particularly for tumor treatment.
The delivery of radio frequency energy to target regions within solid tissue is known for a variety of purposes of particular interest to the present invention, radio frequency energy may be delivered to diseased regions in target tissue for the purpose of tissue necrosis. For example, the liver is a common depository for metastases of many primary cancers, such as cancers of the stomach, bowel, pancreas, kidney and lung. Electrosurgical probes for deploying multiple electrodes have been designed for the treatment and necrosis of tumors in the liver and other solid tissues. See, for example, the electrosurgical probe described in published PCT application WO 96/29946.
The probes described in WO 96/29946 comprise a number of independent wire electrodes which are extended into tissue from the distal end of a cannula. The wire electrodes may then be energized in a monopolar or bipolar fashion to heat and necrose tissue within a precisely defined volumetric region of target tissue. In order to assure that the target tissue is adequately treated and limit damage to adjacent healthy tissues, it is desirable that the array formed by the wire electrodes within the tissue be precisely and uniformly defined. In particular, it is desirable that the independent wire electrodes be evenly and symmetrically spaced-apart so that heat is generated uniformly within the desired target tissue volume. Such uniform placement of the wire electrodes is difficult to achieve when the target tissue volume has non-uniform characteristics, such as density, tissue type, structure, and other discontinuities which could deflect the path of a needle as it is advanced through the tissue.
Referring now to FIGS. 1-5, a shortcoming of electrosurgical probes of the type described in WO 96/29946 will be discussed. Such electrosurgical probes 10 typically comprise a cannula 12 having a plurality of resilient, pre-shaped electrodes 14 therein. The electrodes 14 may be mounted at the distal end of a reciprocatable shaft 16, and the electrodes 14 will be shaped so that they assume an arcuate shape to produce an everting array when the electrodes are advanced from the cannula 12 into solid tissue, as illustrated in FIGS. 4 and 5. With prior electrode probes, such as the illustrated probe 12, the electrodes 14 have been received within lumen 18 of the cannula 12. The electrodes have had circular cross-sections, and no provisions have been made to maintain the individual electrodes 14 in any particular ordered fashion within the cannula. Usually, a random pattern of electrodes 14 exist within the cannula 12, as shown in FIGS. 1 and 2. When electrodes 14 are initially present in such a random pattern (i.e. prior to distal deployment into tissue), the electrodes will adopt a similar random pattern or configuration when first entering into tissue T. When the electrode pattern is non-uniform at the time of first entering into tissue, the non-uniformity will be propagated as the electrodes are fully deployed, as illustrated in FIG. 4. Such a random, irregular pattern is undesirable since it results in non-uniform heating and tissue necrosis.
It would be desirable to provide improved electrosurgical probes of the type described in WO 96/29946, where the individual electrodes 14' are maintained in a uniform pattern within the cannula 12, as illustrated in FIG. 3. In particular, the electrodes 14' should be equally circumferentially spaced-apart and preferably axially aligned with each other within the cannula so that they will follow uniform, equally spaced-apart lines of travel as they penetrate into tissue, as shown in FIG. 5. It will be appreciated that the initial point at which the electrodes penetrate tissue is critical to maintain proper spacing of the electrodes as they penetrate further into the tissue. Should electrodes be misaligned when they first enter the target (i.e. emerge from the cannula) tissue, they will almost certainly remain misaligned as they penetrate further into the tissue. Moreover, the individual electrodes will generally not be steerable or capable of being redirected within the tissue, so there are few options for correcting the configuration after the needles have first penetrated into the tissue. In contrast, by properly aligning the electrodes prior to and at the time they first enter into tissue from the cannula, the proper electrode pattern can be assured as the electrodes deploy radially outwardly into the tissue. It would be still further desirable to provide electrosurgical probes and methods for their deployment which would provide for improved propagation through tissue having non-uniform characteristics. Even when the electrodes are disposed in a symmetrical pattern at the outset of deployment, the electrode paths can be deflected or deviated when the electrodes encounter relatively hard or dense regions within the tissue. It would be beneficial if the electrodes were capable of passing through such regions with minimum or no deflection.
For these reasons, it would be desirable to provide improved electrosurgical probes having multiple, tissue-penetrating electrodes. In particular, it would be desirable to provide improved electrosurgical probes and tissue ablation apparatus of the type described in WO 96/29946, where the electrodes are configured within the probes so that they deploy in a uniform, evenly spaced-apart manner as they penetrate into tissue to be treated, thus overcoming at least some of the shortcomings noted above.